1. Field of the Invention
The present invention relates to a blue electroluminescence compound and an organic electroluminescence display device, and more particularly, to a blue electroluminescence compound having improved light emitting efficiency and brightness and the organic electroluminescence display device using the same.
2. Description of Related Art
There is need to develop a display device having high performance according to the advancement of the information-communication industry. This display device is divided into two kinds, a light emitting type and a non-light emitting type. There are a cathode ray tube (CRT), an electroluminescence display (EL), a light emitting diode (LED), and a plasma display panel (PDP) as a light emitting type. Also, there is liquid crystal display (LCD) as a non-light emitting type.
The light emitting type display device and the non-light emitting type display device have basic characteristics of operating-voltage, consumption power, brightness, contrast, response time, life span and indication color. But, the liquid crystal display used frequently has problems of late response time, low contrast, and dependence of visual angle, etc.
It is difficult to apply a light emitting diode for an electroluminescence display device because the light emitting diode uses inorganic materials having mainly a crystal type. Also, in case of the electroluminescence display device using the inorganic materials, it has problems in that it needs 200 V of an operating-voltage and its production cost is high. But the display device using the light emitting diode has a rapid response time, and a good brightness, and is self-light emitting type without requiring a back light. Accordingly, it is hopeful that the display device using the light emitting diode will lead to advanced next-generation devices.
The electroluminescence display device is divided into an organic electroluminescence display device and an inorganic electroluminescence display device according to the material for forming the light emitting layer.
The organic electroluminescence display device is better with regard to brightness, operating-voltage and response time than the inorganic electroluminescence display device, and has a benefit of multi-colorization because the organic electroluminescence display device is a self-light emitting device which emits light by being electrically excited.
Also, this device has excellent properties of high brightness, rapid response time, wide visual angle, and multi-color emitting as a thin type because of the conductive device emitting in a low voltage direct current of a few volts.
The organic electroluminescence display device can be applied to a full color flat display.
The conventional organic electroluminescence display device has an anode on the upper portion of the substrate, and a hole transport layer, a light emitting layer, and an electron transport layer formed in this order on the upper portion of the anode. The hole transport layer, the light emitting layer and electron transport layer are made of an organic thin film consisting of organic compounds.
The operating method of the organic electroluminescence display device having the structure as cited above is described as below.
A hole injected from the anode is transferred to the light emitting layer via the hole transport layer when a voltage is provided between the anode and the cathode. While the electron is injected into the light emitting layer via the hole transport layer from the cathode, an exciton is produced by recombining carriers with each other in the region of the light emitting layer. This exciton is changed into a ground state from an excited state, a fluorescence molecule of the light emitting layer is emitted due to a change of the state, and an image is formed.
On the other hand, the Eastman Kodak company has developed an organic electroluminescence display device using a low molecule aromatic diamine and aluminium complex as the material for forming the light emitting layer in 1987 (Appl. Phys. Lett. 51, 913, 1987).
Diphenylanthracene, tetraphenylbutadiene, and distilylbenzene have been developed as the blue electroluminescence material, but it is known that these compounds are crystallized due to the poor stability of the thin film.
Idemitsu Company has developed a diphenyldistillyl group having an improved thin film stability because the phenyl group prevents the crystallization of the compounds (H. Tokilin, H. Higashi, C. Hosokawa, EP 388, 768 (1990)), and Kyushou University has developed a distilylanthracene derivative having an improved thin film stability by having the electron withdrawing group and the electron donating group (Pro. SPIE, 1910, 180 (1993)).
However, because the above electroluminescence compounds have a lower light emitting efficiency than other conventional electroluminescence compounds and there is need to develop the stability of the thin film of the display device, it is required to develop new blue electroluminescence compounds.
To overcome the problems described above, it is an object of the present invention to provide a blue electroluminescence compound comprising a spirobifluorene having excellent light emitting efficiency and good brightness.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
The above and other objects of the present invention are further achieved by providing a blue electroluminescence compound comprising a triarylsilphenyl group.
The above and other objects of the present invention may also be achieved by providing an organic electroluminescence display device using one of the blue electroluminescence compounds provided above.